Typically, in the drilling of a well, a borehole is drilled from the earth's surface to a selected depth and a string of casing is suspended and then cemented in place within the borehole. A drill bit is then passed through the initial cased borehole and is used to drill a smaller diameter borehole to an even greater depth. A smaller diameter casing is then suspended and cemented in place within the new borehole. Generally, this is repeated until a plurality of concentric casings are suspended and cemented within the well to a depth which causes the well to extend through one or more hydrocarbon producing formations.
Oftentimes, rather than suspending a concentric casing from the bottom of the borehole to the surface, a liner may be hung either adjacent the lower end of a previously suspended and cemented casing, or from a previously suspended and cemented liner. A liner hanger is used to suspend the liner within the lower end of the previously set casing or liner. A setting tool disposed on the lower end of a work string is releasably connected to the liner hanger that is coupled with the top of the liner. The liner hanger, liner, setting tool, and other components are generally part of a liner hanger assembly.
Another component, such as a liner top packer, may also be part of the liner hanger assembly, which may be used to seal the liner in the event of a poor cement job or to prevent gas flow while the cement sets. Typically, the liner top packer is set down on top of the liner hanger, and the liner top packer is set by the setting tool to seal the annulus between the liner and the previously set casing or liner. Liner top packers run with liner hangers typically include a tubular member with a bore in it that is coupled with the top end of the packer.
This tubular member is commonly referred to as a polished bore receptacle (“PBR”) or a tieback receptacle (“TBR”). Because the liner does not run to the surface, the liner hanger has the ability to receive the PBR or TBR to connect the liner with a string of casing that extends from the liner hanger back to the surface. There is typically a seal or seal stack between the PBR and the body of the packer that allows axial motion of the PBR relative to the liner top packer body. A standard seal stack includes a plurality of annular spaced seals that fit within the interior of the PBR. Often, a PBR is coupled into an upper end of the packer, and production tubing is strung into the PBR with an appropriate seal to prevent leakage between the interior of the PBR and the production tubing.
Various types of liner hangers have been proposed for hanging a liner from a casing string in a well. Most liner hangers are set with slips activated by the liner hanger running tool. Liner hangers with multiple parts pose a significant liability when one or more of the parts become loose in the well, thereby disrupting the setting operation and making retrieval difficult. In addition, wellbores often have tight spots and dog legs through which the liner hanger maneuvers, increasing the risk of the liner hanger becoming stuck or coming apart. Other liner hangers and running tools cannot perform conventional cementing operations through the running tool before setting the liner hanger in the well.
Other liner hangers have problems supporting heavy liners with the weight of one million pounds or more. Some liner hangers successfully support the liner weight, but do no reliably seal with the casing string. After the liner hanger is set in the well, high fluid pressure in the annulus between the liner and the casing may blow by the liner hanger, thereby defeating its primary purpose.
Another significant problem with some liner hangers is that the running tool cannot be reliably disengaged from the set liner hanger. This problem with liner hanger technology concerns the desirability to rotate the liner with the work string in the well, then disengage from the work string when the liner hanger has been set to retrieve the running tool from the well. Prior art tools have disengaged from the liner hanger by right-hand rotation of the work string, although some operators for certain applications prefer to avoid right-hand rotation of a work string to release the tool from the set liner. In addition, operators are presented with the problem of debris entering the running tool during disengagement of the liner.
Accordingly, there exists a need for an improved downhole tool that has improved torque to wash and ream through tight spots and dog legs within the wellbore, that may avoid pre-setting while running, and that is able to more effectively maneuver through tight areas in the wellbore.